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Questions tagged [radio-frequency]

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Why do sensors that emit higher frequency signals give more accurate data?

I am doing a technical presentation about RADAR and LiDAR. I understand that LiDAR is several times more accurate and capable of producing really detailed 3-D maps of their surroundings, while RADARs ...
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1answer
36 views

Best cantenna reflector type

If the reflector (closed end) of cantenna is shaped as parabolic dish, will it perform better than one with a flat reflector?
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1answer
23 views

Why is $Q$ factor an important quantity for electrical oscillations transmitting radio waves?

My textbook says that "$Q$ factor is an especially important quantity for electrical ossicilations trasnmitting radio waves. When selecting radio and television stations it is essential that the ...
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1answer
29 views

How can I calculate the total rotation a detuned pulse will apply a nuclear spin?

I'm trying to model the effect a radiofrequency pulse will have on a nuclear spin at different detunings. The pulse has a sech lineshape, a pulse area (time integral of the pulse envelope) of $\frac{π}...
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3answers
58 views

Can a lens be used at radio frequency?

Lenses and Antennas are two means of manipulating EM waves. While antennas are predominantly used at RF / Microwave frequencies, Lenses are used for optical/IR regions of the spectrum. I understand ...
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0answers
24 views

Are there Lasers in wavelenght of UHF or radio frequency?

how exists lasers in many wavelength in electromagnetic spectrum, like UV, VIS and IR. I don't know nothing about others wavelength as X-ray or radio frequency.
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2answers
57 views

How can Line of Sight work?

How can a mobile phone work inside a closed room with no openings if Line of Sight requires no obstacles between the receiver and transmitters? I know you may think it's not a Physics question but ...
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2answers
71 views

Why radio waves from radio-stations don't interfere with each other?

I know that radiowaves from radiostations are modulated either F.M or A.M . Lets suppose they are F.M and one has carrier wave frequency of 100 Hz and other 200 Hz they have F deviation of 20Hz/V . ...
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1answer
30 views

Does attenuation to RF waves increases with frequency?

I heard somewhere that RF waves at high frequency such as above 2GHz face more attenuation while passing through air, buildings and due to humidity as compared to 800Mhz and 2) Waves at 30-40GHz ...
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2answers
79 views

How are RF Waves transmitted?

What is the mode of transmission for RF waves at 1800 MHz. Is it ground wave propagation, Line of Sight Propagation or Atmospheric reflection (from ionosphere). What are the different ways for ...
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1answer
42 views

Why is power density of RF waves measured in m2?

Why is power density of RF waves measured in m2 or cm (Area) and not in cm3 or m3 (volume) ? I mean aren't those waves travelling (radiating) in 3D space? I am new to this topic so please pardon ...
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Electromagnetic Waves and GPS

If the global positioning system functions through radio waves, but radio waves are reflected in the ionosphere, then how do these electromagnetic waves reach the satellites?
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4answers
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What's the physics behind XKCD #2027 (time between lightning flash and radio wave burst)?

XKCD usually has solid (and often contemporary) science behind it. Lightning Difference, #2027 one says: Q: What’s that trick for telling how many miles away lightning is? A: Just count the ...
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1answer
76 views

Radio waves collision versus waves in a pond collision

Please see the attached picture: We are trying to show an image to visualize radio wave collision and interference with regards to Maritime AIS Technology. What do colliding radio waves have in ...
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6answers
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Why put a radio telescope in space instead on the Moon?

Why are we not building a space-based radio telescope? If a lunar radio telescope is hard to build, why not a space-based radio telescope? It could be an interesting tool, I presume. Thus, what could ...
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2answers
5k views

What is the scientific explanation for radio waves bending around the Earth?

The experiment This experiment is documented in a documentary called Convex Earth. The exact location the following information is taken from starts at 14:25. High frequency directional antennas are ...
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1answer
112 views

Why radio waves can pass through walls but not infrared waves?

My physics teacher told that infrared waves are not passing through walls due to rayleigh scattering,but rayleigh scattering increases with increase in wavelength,then why radio waves are passing ...
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1answer
34 views

How do electrons in a conductor physically respond to radio waves?

If a radio wave hits a thick piece of metal, it's my understanding that the metal will for the most part reflect the wave. What I'm unclear about is how the electrons flow in a metal that's being ...
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1answer
164 views

Is Nylon RF transparent?

I was doing a research on which type clothes blocks the Radio frequency. Please also list the experiments which can be performed to determine such clothes/ materials.
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Transport Networks and Information Distribution Protocols

i am new in matlab and i don't have any idea about it. the professor gave us this. really i don't understand. :( arryf A , s=cosAt+cos3t define a sum of cosine waves"number of waves is the last ...
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A shaped pulse as a sum of rectangular pulses

I have a pulse with lineshape $L(ω)=\frac{1}{π}\frac{\frac{1}{2}Γ}{((ω−ω_0)^2+(\frac{1}{2}Γ)^2)}$ in the frequency domain where $\Gamma$ is the pulse width and $\omega_0$ is the resonant frequency ...
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1answer
29 views

Why do satellite dish come in many different sizes?

Is it to do with how many photons can be absorbed in a given area? more surfaces mean more photons are absorbed but does it translate to better quality? btw can a single atom be as good as the largest ...
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4answers
112 views

Can the equation $E = h\nu$ be used not only for light, but for radio waves? (Since they are all part of the electromagnetic spectrum)

Can the equation $E = h\nu$ (or $E = hf$) be used to find the energy of the particles from the electromagnetic spectrum? I mean, for example light is part of the EM, a radio wave is also part of the ...
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0answers
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Effect of a Lorentzian pulse on a non-resonant spin particle

I'm looking into rotation of a nuclear spin particle using a pulse with a Lorentzian lineshape. If the pulse has an area of $\frac{\pi}{2}$ and the nuclear spin frequency is on resonance with the ...
0
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1answer
38 views

Modelling a radiofrequency pulse

I'm looking into NMR at the moment and am trying to work out a way of modelling the action of a radiofrequency pulse on nuclear spins. Specifically, if I apply a pulse to rotate the spin by $\pi/2$ I ...
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0answers
136 views

advantages or disadvantages of pulsed laser vs continuous-wave (CW) laser

What are the advantages and disadvantages of pulsed vs CW laser? Does pulsed laser have more power compared to CW laser, or it is vice versa? If I have to guess, for long distance communication, ...
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2answers
81 views

Communications: Ground wave Propagation

(I wasn't having any tag for this question(Example: Communication-Systems, Modern-physics.)) I was studying ground wave propagation, my book writes the lines about it without explaining it. I really ...
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3answers
67 views

L-band for search radars?

I'm making my way through the Linesman-related section's of Gough's Watching the Skies. Linesman was developed to counter the carcinotron jammer. The main solution was the Type 85, which had 12 ...
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2answers
1k views

Why doesn't the ${\rm H}_2$ molecule have a permanent dipole while the neutral ${\rm H}\,{\rm\small I}$ has one?

According to the National Radio Astronomy Observatory, the $21\,{\rm cm}$ line of hydrogen can be emitted by the neutral hydrogen atom due to the magnetic interaction between the spins of the proton ...
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2answers
309 views

Reflection of radio waves at an obstacle with size half wavelength

I'm following a course about communication technology and the professor said the following multiple times: "A radio/EW-wave is reflected at an obstacle which is higher/larger than than half of the ...
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2answers
123 views

(Please Explain) Clarification on extraterrestrial communication with radio waves

I just want to get some clarifications regarding the transmission and receiving of a radio waves between planets as a means of communication with aliens for story building. Is it better to transmit ...
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1answer
96 views

Why don't radio waves ruin electronics?

Out of curiosity, I estimated the voltage amplitude for typical visible light. Wikipedia says that sunlight hits the earth at about $1000 W / m^2$. The intensity of an electric field is given by $$I =...
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1answer
242 views

Does a Faraday Cage need to be sealed to block RF?

I was watching a program on shoplifting and there were things called booster bags shown, which blocked a security tag which acts as an LC resonator when put between the security towers, causes the ...
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1answer
229 views

Power losses for electromagnetic waves radiation in copper wire with high frequency current [closed]

How to calculate electric power losses to radiation of electromagnetic waves in copper wire with high-frequency current? For example, I have a copper wire with known diameter and length and I send ...
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0answers
27 views

Magnet on a piezo - Can this oscillating field give me a radio transmitter?

I can read on wikipedia that radio waves are of frequency 3kHz-3THz. I know that piezoelectric actuator can reach eg. 20 kHz. What would happen if I put a small neodymium magnet on a piezoelectric ...
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1answer
146 views

How to convert RF absorption rate (SAR) values to electric field values?

I'm currently reading a bunch of journal articles that describe biological effects of electromagnetic fields. They often refer to the field in terms of specific absorption rate (SAR) values (W/kg). ...
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1answer
46 views

If inductive reactance increases with frequency why do tesla coils have coils?

So I was reading about the special properties of radio frequencies. Specifically I read this: "In contrast, RF current can be blocked by a coil of wire, or even a single turn or bend in a wire. This ...
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2answers
3k views

Why do I need to adjust TV antenna on the roof for better video quality?

I find it a annoying and a pain to climb up to the roof and adjust the TV antenna so that I can watch my favorite TV program without distortion. I am not using satellite service which requires a dish ...
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0answers
143 views

Weird RF manipulation in electrical circuits

I have recently seen an EEVblog tear-down of a spectrum analyzer, and it contained a few odd looking bits such as this: This got me thinking, would it be possible to create an entire electrical ...
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0answers
25 views

Radio vs X-ray pulsar timing

The detection and timing of pulsars is a common goal in astronomy (eg.1, 2). Typically these observations are done in the radio. I appreciate that observations are taken in the X-ray as well, but is ...
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3answers
664 views

What are crystals used for in radio?

What are crystals used for in radio? I think I sort of know the answer to this but I would like a more detailed explanation. To my current understanding, piezoelectric crystals are used to modulate ...
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2answers
217 views

Transmitter and receiver precision

How precise can we make a transmitter's signal and then detect signals? ... And if different parts of the spectrum have different limits.
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1answer
86 views

How do Antennas receive information?

Do wireless signals (Wifi router, radio, telephone) send their information in single "blinks" or in a continuous wave with frequency modulation or Amplitude modulation? If a radio for example needs ...
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1answer
151 views

About The foxhole radio : coil rotation times, whether capacitor's needed

I recently tried to make a DIY foxhole radio. Althogh I made it according to the manual(140times coil rotated, ground(220V), blued razor blade, pencil core and antenna(just a steel stick about 1 meter)...
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2answers
288 views

Why are only the extremely low frequencies of electromagnetic radiation able to penetrate the earth and sea?

Wikipedia classifies ELF (Extremely Low Frequency) radiation as between 3 Hz and 300 Hz, and ULF (Ultra Low Frequency) from 300 Hz to 3 kHz. Both ranges can penetrate the earth and sea. What is the ...
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1answer
120 views

Would my house's wall stop gamma rays?

I'm wondering if there is a material which is able to stop all the electromagnetic spectrum's radiations. Something able to stop every electromagnetic radiation from the ones with the lowest frequency ...
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1answer
254 views

Bistatic radar equation for moving objects

From my understanding, and correct me if I'm wrong, the bistatic radar equation assumes that the transmitter and the receiver are separated by a distance $L$, and that the transmitter and receiver are ...
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1answer
59 views

Sideband frequencies

In amplitude modulation when carrier signal and base band signals are mixed, side band frequencies are generated. Upper side band frequency is $f_c+f_m$ and lower side band frequency is $f_c-f_m$. ...
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Why does Skywave only work for a small frequency band?

So it is often said that waves in the HF band (3-30MHz) use skywave propagation to beam signals around the curvature of the Earth. My question is why is there this narrow limit to what is able to ...
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1answer
69 views

Do we get radiowaves if the antenna is a loop or a coil?

What happens if we use an antenna which is not a straight wire, i.e a loop or a coil? do we get EMR? Now, if we do, what is the difference between this loop and the primary winding of a transformer? ...